1. The density of ethanol is .78 g/mL.
Calculate the volume of 94.4 g of ethanol.
A. we have 94.4 g of ethanol
B. we want its volume
C. 94.4 g .
.78 g/mL = 121 mL
2. Determine the density of a 21.232 g cylinder whose radius is 1.42 cm and whose height is 10 cm.
A. we have 21.232 g
B. we want to first find the cylinder’s volume in order to find its density
C. volume pi(1.42)2(10) = 63 cm
D. density=21.232 g
63 cm^3 = 0.34 g/cm^3
The Rules of DIMENSIONAL ANALYSIS:
1. Determine what you have.
2. Determine what you want.
3. Put what you have on top and what you want on bottom.
4. Always put the starting unit on the bottom of the next conversion.
5. ALWAYS use units.
Dimensional Analysis Conversion Practice Problems:
1. Convert 345 cm to miles.
A. we have 345 cm
B. we want our answer in meters
C. 345 cm1 in.1 ft1 mi . = .0020 mi
1 2.54 cm 12 in 5,280 ft
2. Convert 2 yrs to weeks.
A. we have 2 yrs
B. we want our answer in wks
C. 2 yrs12 months4 wks7 days = 672 wks
1 1 yr 1 mnth 1 wk
3. Convert 54 mi/h into m/s (given: 1 km = 0.621 mi).
A. we have 54 mi/h
B. we want our answer in m/s
C. 54 mi1 km1000 m1 hr1 min
1 hr .621 mi 1 km 60 min 60 sec = 24 m/s (after determining # sig figs)
Section 2-3
Accuracy vs. Precision
Accuracy - closeness of measurements to the correct value of quantity measured.
Precision - repeated trials give the same answer; consistent; in the same range multiple times.
Calculating Percentage Error
Experimental Value - Actual Value
% error = Actual Value X 100
SIGNFIANT FIGURE: a measurement that consists of all the digits you know with certainty plus 1 final digit, which is somewhat uncertain or is estimated.
The rules of "Sig Figs":
1. All non-zero digits are significant (457.3 = 4)
2. Zeros appearing between nonzero digits are significant (707 =3)
3. Leading zeroes are NEVER sig figs (005=1)
4. Trailing zeroes are significant if a decimal is present (200=1, but 200. = 3)
5. Exact numbers have infinite sig figs
1 dozen = 12: not open to interpretation
Any measurement: open to interpretation
Remember that...
When adding or subtracting decimals,
the answer must have the same # of digits to the right of the decimal point as there are in the measurement having the fewest digits to the right of the decimal point.
For multiplication or division,
the answer can have no more sig figs than there are in the measurement with the fewest number of sig figs.
SCIENTIFIC NOTATION
M x 10^n
M = A number >1<10
n = whole # found by counting the number of places to the decimal point
Proportions
Direct proportion: dividing one by the other gives a constant value
y = kx
Inverse proportion: multiplying one by the other gives a constant value
xy = k
The Scientific Method: A logical approach to solving problems by…
Section 2-2
SI (system international) base units:
- Mass – Kilogram (kg)
Mass is NOT the same as weightSI derived units (combinations of base units):
Conversions to know:
Metric Prefixes:
Density: the ratio of mass to volume
mass
volume = density
Density Practice Problems:
1. The density of ethanol is .78 g/mL.
Calculate the volume of 94.4 g of ethanol.
A. we have 94.4 g of ethanol
B. we want its volume
C. 94.4 g .
.78 g/mL = 121 mL
2. Determine the density of a 21.232 g cylinder whose radius is 1.42 cm and whose height is 10 cm.
A. we have 21.232 g
B. we want to first find the cylinder’s volume in order to find its density
C. volume pi(1.42)2(10) = 63 cm
D. density=21.232 g
63 cm^3 = 0.34 g/cm^3
The Rules of DIMENSIONAL ANALYSIS:
1. Determine what you have.
2. Determine what you want.
3. Put what you have on top and what you want on bottom.
4. Always put the starting unit on the bottom of the next conversion.
5. ALWAYS use units.
Dimensional Analysis Conversion Practice Problems:
1. Convert 345 cm to miles.
A. we have 345 cm
B. we want our answer in meters
C. 345 cm 1 in . 1 ft 1 mi . = .0020 mi
1 2.54 cm 12 in 5,280 ft
2. Convert 2 yrs to weeks.
A. we have 2 yrs
B. we want our answer in wks
C. 2 yrs 12 months 4 wks 7 days = 672 wks
1 1 yr 1 mnth 1 wk
3. Convert 54 mi/h into m/s (given: 1 km = 0.621 mi).
A. we have 54 mi/h
B. we want our answer in m/s
C. 54 mi 1 km 1000 m 1 hr 1 min
1 hr .621 mi 1 km 60 min 60 sec = 24 m/s (after determining # sig figs)
Section 2-3
Accuracy vs. Precision
Accuracy - closeness of measurements to the correct value of quantity measured.
Precision - repeated trials give the same answer; consistent; in the same range multiple times.
Calculating Percentage Error
Experimental Value - Actual Value
% error = Actual Value X 100
SIGNFIANT FIGURE: a measurement that consists of all the digits you know with certainty plus 1 final digit, which is somewhat uncertain or is estimated.
The rules of "Sig Figs":
1. All non-zero digits are significant (457.3 = 4)
2. Zeros appearing between nonzero digits are significant (707 =3)
3. Leading zeroes are NEVER sig figs (005=1)
4. Trailing zeroes are significant if a decimal is present (200=1, but 200. = 3)
5. Exact numbers have infinite sig figs
1 dozen = 12: not open to interpretation
Any measurement: open to interpretation
Remember that...
When adding or subtracting decimals,
the answer must have the same # of digits to the right of the decimal point as there are in the measurement having the fewest digits to the right of the decimal point.
For multiplication or division,
the answer can have no more sig figs than there are in the measurement with the fewest number of sig figs.
SCIENTIFIC NOTATION
M x 10^n
M = A number >1<10
n = whole # found by counting the number of places to the decimal point
Proportions
Direct proportion: dividing one by the other gives a constant value
y = kx
Inverse proportion: multiplying one by the other gives a constant value
xy = k